Pressure effects of genuine organic crystalline ferromagnet possessing intermolecular contacts between nitroxide oxygen and methyl hydrogen atoms

We have found the pressure-induced (1) periodical down–up variation of transition temperature (Tc), (2) ferro- to antiferro-magnetic transition and (3) reduction of the magnetic lattice dimensionality in a genuine organic crystalline bulk-ferromagnet p-Cl–C6H4–CHN-TEMPO (Tc=0.28 K) with spin polarizations on intermolecular contacts between the nitroxide oxygen and methyl hydrogen atoms (C–H⋯O–N contacts). These phenomena can be understood by the pressure-induced rotation of the methyl moiety relevant to the interaction-mechanism through C–H⋯O–N contacts.